The present invention relates to an intake air flow control apparatus of internal-combustion engine and, more particularly, to an intake air flow control apparatus of internal-combustion engine which, during deceleration, controls the supply of a required quantity of intake air to an engine which is capable of changing intake or exhaust valve lift characteristics.
The engine, when in a state of deceleration and especially with the throttle valve fully-closed, is likely to be reversely driven by the wheels through a power transmission system, thereby decreasing the pressure in the intake pipe. With this pressure decrease, a negative pressure will be built up in the intake air passage at the downstream side of the throttle valve, allowing the lubricating oil in the oil pan of the engine to work up into a combustion chamber in a cylinder, and accordingly, as is well known, causing an adverse effect on oil consumption. In an internal-combustion engine having an improved piston ring structure or a decreased number of piston rings for the purpose of improving the dynamic characteristics and thermal efficiency of the engine, the improvement in the piston ring structure and the decrease in the number of the piston rings cause an increase the amount of lubricating oil entering the combustion chamber, resulting in a further increase in oil consumption.
To prevent such an increase in oil consumption, there has been suggested in Laid-Open Japanese Patent Publication No. 61-27243 an intake air flow control apparatus for controlling the quantity of intake air preset for each engine speed and being supplied to the downstream side of the throttle valve during the period of engine deceleration for the purpose of increasing the absolute pressure in the intake pipe.
However, this intake air flow control means is inadequate to prevent the oil from working up into the combustion area in the case of a vehicle provided with a so-called variable valve timing mechanism which is capable of changing the intake or exhaust valve lift characteristics of the engine. That is, the variable valve timing mechanism is designed to automatically vary the valve timing to a low-speed valve timing for operation in low- and medium-speed ranges and to a high-speed valve timing for operation in a high-speed range, thereby ensuring the production of a high power throughout a wide range from low to high speeds without decreasing the power in the low-speed range. The applicant of the present invention has previously proposed a valve timing change control (a patent applied for Apr. 1, 1988) for engines capable of changing the valve timing of at least one of the intake valve and the exhaust valve to a low-speed valve timing (Low-speed V/T) suitable for a low-speed range and to a high-speed valve timing (High-speed V/T) suitable for high-speed range. In this engine, the valve timing change control is adapted to change the valve timing at the time two values, read according to an engine operating condition, nearly coincide with each other, from a basic fuel quantity map for low-speed V/T set in accordance with a low-speed V/T and a basic fuel quantity map for high-speed V/T set in accordance with a high-speed V/T, and to determine the quantity of fuel to be supplied to the engine on the basis of the basic fuel quantity for high-speed V/T when a high-speed V/T is demanded and also on the basis of the basic fuel quantity for low-speed V/T when a low-speed V/T is demanded.
In a motor vehicle provided with an engine having such a variable valve timing mechanism, the engine is subjected to a change in pumping efficiency with the change of the valve timing, and accordingly the negative pressure produced during deceleration and the engine speed characteristics also vary, thus changing the amount of intake air required for maintaining a nearly constant absolute pressure in the intake pipe during deceleration.